1. Field of the Invention
The present invention relates to an organic electronic device and a method for producing the same. Particularly, an organic electronic device including an organic light emitting device such as an organic electroluminescent element, an organic transistor, an organic solar battery or the like, and a method for producing the same.
2. Description of the Related Art
Development of an organic electronic device is expected to a wide range of elementary elements including an organic light emitting device such as an organic electroluminescent elements (hereinafter referred to as an organic EL element), an organic transistor, an organic solar battery or the like and uses.
An organic EL element is a charge injection type self light emitting device, utilizing the light emission generated at the time of re-coupling an electron and a positive hole reaching at a light emitting layer. Such an organic EL element has been developed actively since 1987 when T. W. Tang, et al. proved that an element comprising laminated thin films of a fluorescent metal chelate complex and a diamine based molecule emits a light of a high luminance with a low driving voltage.
The element configuration of the organic EL element basically comprises cathode/organic layer/anode. The organic layer thereof in general has a two layer structure comprising a light emitting layer and a positive hole injection layer, or a three layer structure comprising an electron transporting layer, a light emitting layer and a positive hole transporting layer. In the organic EL element, it is necessary to supply charges (positive hole and electron) to a light emitting material to be the luminescent center efficiently and quickly. For that purpose, a charge transporting material is contained in the light emitting layer, a positive hole transporting layer is provided between the anode and the light emitting layer, or an electron transporting layer is provided between the cathode and the light emitting layer.
According to the organic EL element, in order to obtain a high luminous efficiency, it is necessary to efficiently inject charges (positive hole and electron) from the electrode to the organic layer, however, since the energy gap between the anode or the cathode and the organic layer such as the light emitting layer or the like is so large that the charges cannot be injected easily. Therefore, conventionally, the energy gap between the electrode and the organic layer is reduced by providing a positive hole or electron injection layer between the anode or the cathode and the organic layer, or by optimizing the work function of the anode or the cathode.
For example, for a cathode, an alloy of Mg or Li having small work function and relatively stable Ag or Al has been used as an electrode. However, in this case, since Mg or Li having small work function is easily oxidized and unstable, an element deteriorates due to oxidation of an electrode or the like. In addition, in view of a function as a wiring material, an electrode of alloy narrows down the choices of material for the electrode.
Thus, in order to attain a low driving voltage without using a material having a small work function for a cathode, studies has been made to provide an electron injection layer between a cathode and a light emitting layer, wherein an alkali metal or an alkaline-earth metal is used for the electron injection layer. For example, Japanese Patent Application Laid-Open (JP-A) No. Hei. 09-17574 discloses that an electron injection layer contains an alkali metal compound, which is an inorganic compound such as LiF, Li2O or the like. However, since the alkali metal compound of an inorganic compound has an insulating property, it is necessary to form a very thin layer thereof. Hence, it is hard to form a layer by a vapor deposition, thus, it is difficult to obtain an element which exhibits stable performance even though the element is used repeatedly.
Also, for example, JP-A No. 2000-91078 discloses an electron injection layer made from an organic salt or an organometallic complex of an alkali metal or an alkaline-earth metal. JP-A No. 2000-243569 discloses that an electron injection layer made of an organometallic compound containing an alkali metal. JP-A No. 2003-303691 discloses a second cathode containing metal carboxylic acid containing an alkali metal or an alkaline-earth metal. Also, JP-A No. Hei. 11-233262 discloses an organic layer adjacent to a cathode is composed of an organometallic complex compound containing at least one kind selected from the group consisting of an alkali metal ion, an alkaline-earth metal ion and a rare-earth metal ion, and the cathode is made of a metal which can reduce the metal ion contained in the complex compound to the metal under vacuum condition. Further, JP-A No. Hei. 10-270171 discloses attainment of a low driving voltage by having an organic compound layer doped with a metal which functions as a donor (electron donating) dopant at an interface of a cathode so as to lower the energy gap upon electron injection. However, in all of the prior arts, a layer needs to be formed by a vapor deposition under vacuum condition, therefore, the production process takes a long time.
Other than the organic EL element, as a representative example of an organic electronic device using an organic material having certain degree of carrier, mobility, there may be an organic solar battery or the like.
The organic solar battery utilizes, so to speak, a mechanism opposite to an organic EL element. That is, the most basic constitution of the organic solar battery is the same as that of an organic EL element, which is a structure having an organic thin film having a two layer structure disposed between electrodes (see “App. Phys. Lett.”, (1986), Vol. 48, Number 2, p. 183-185). An electromotive force can be obtained by utilizing photocurrent which is generated when the organic thin film absorbs light. The electric current at this time may be considered that a carrier generated by light flows utilizing the carrier mobility of an organic material. If a charge injection barrier of the organic material and the electrodes lowers, an electromotive force can be obtained more efficiently.
An organic transistor, which is another representative example of the organic electronic device, is a thin film transistor using an organic semiconductor material comprising an organic polymer or an organic small molecule compound having a π conjugated system for a channel area. A general organic transistor comprises a substrate, a gate electrode, a gate insulating layer, source and drain electrodes and an organic semiconductor layer. In an organic transistor, switching is performed by changing a voltage (gate voltage) applied to the gate electrode so that a quantity of electric charge of an interface of a gate insulating layer and an organic semiconductor layer is controlled and a current value between a source electrode and a drain electrode is changed.
However, when the organic semiconductor material used in the organic transistor is employed, a charge injection barrier between the organic semiconductor material and the source electrode or the drain electrode is large, thus causing a problem in driving an element. Also, if a charge injection barrier between the organic semiconductor layer and the source electrode or the drain electrode can be lowered, it is expected that an on-current value of the organic transistor improves and an element characteristic stabilizes.
On the other hand, an organic electronic device such as the organic EL element or the like having the light emitting layer, the charge transporting layer or the like foamed by a wet film forming method (spin coating method, printing method, ink jet method or the like), which comprises solving or dispersing a polymer organic compound having luminescence, charge transporting property or the like in a solvent and applying on a substrate, is proposed. The wet film forming method, in which a material is applied on a substrate using a solvent, does not need a large-scale vapor deposition apparatus in comparison with a vacuum vapor deposition method and can expect simplification of a production process. In addition, the wet film forming method has the advantages such as high usability efficiency of material, low cost and capability of increasing area of a substrate. The wet film forming method also has the advantage that materials are easily coated separately in a line, for example, RGB or the like of an organic EL element.